High intensity discharge lamps (HID) lamps are widely used in various structures having high ceilings such as gymnasiums, warehouses, commercial buildings and the like. HID lamps typically utilize metal halide, mercury vapor, high or low pressure sodium depending on the application and lighting characteristics desired. These lamps may range from 500 to 1,000 Watts for example, so that the buildings wherein such HID lamps are utilized are well lit. However, one problem with such HID lamps is the significant energy consumption occurring in these lamps.
In order to maximize downward lighting, bell-shaped reflectors are typically utilized to fit over the base of the HID lamps. The lamps are screwed into a power supply in order to power the lamp. The reflectors are typically made of polished aluminum or similarly reflective lightweight material. The opposite lower end of the reflector may be opened or may be covered with a translucent lens to further diffuse lighting emanating from the lamp and provide a substantially attractive appearance.
As an alternative to HID lamps, some commercial applications utilize fluorescent light fixtures, which often have fluorescent tubes with a length of four or eight feet. These tubes are often placed parallel to the floor or substrate to produce a predetermined lumination pattern. Installation and replacement of these types of tubes, particularly eight foot tubes, is often difficult due to the length of the tubes and the electrical connectors being located at distal ends of the tube.
Compact fluorescent lamps have a generally “folded-over” bi-axial design which attached to a light fixture at a single end. Alternatively, such lamps may be helical or corkscrew in nature. Sales of compact fluorescent lamps (CFLs) have increased in volume due to improvements in the performance and reduction of prices in this type of lamp. In addition, the market for CFLs has been spurred on by the integration of lamp and electronic ballast with either a screw-in or bayonet fitting allowing easy replacement of consumable lamp.
The CFLs are produced in various shades of white including “warm white” or “soft white” providing a light very similar to an incandescent bulb; “white”, “bright white” or “medium white” producing a yellowish white light, whiter than an incandescent lamp but still on the warm side; “cool white” emitting more of a pure white tone; and “day light” having a slightly bluish white appearance. Compact fluorescent lamps have two main parts. First, the CFLs utilizes a gas filled tube. Second, the CFLs typically utilize magnetic or electronic ballast. The ballast may be remote from the tube or may be connected to the tube. Electrical energy in the form of an electrical current passes from the ballast through the gas causing it to emit ultraviolet light. The ultraviolet light excites a white phosphorus coating on the inside of the tube emitting a visible light.
Prior art low-bay luminaires utilize compact fluorescent lamps generally in a base up orientation and tilted inside the reflector to extend downwardly from the base. There are several problems with prior art luminaires of this type. First, in the prior art, base-up configurations, the lamp sockets are closely spaced near the top of the reflector creating excessive heat. Accordingly, various prior art luminaires are only rated for 25 degrees Celsius ambient operating temperature. Second, there is always a desire to increase the total lumen output, the sum of light output from nadir to 180° of the luminaire. There is also a desire to increase the total efficiency of the luminaire, which is measured as a percentage of the lamp output by the luminaire. There is also a desire to decrease the amount of uplight emitted from the luminaires since such uplight is only useful with very high reflectant ceilings. Further, there is a desire to decrease the amount of lighting in the glare zone which is defined as the 60 to 90 degree area. There is also a desire to increase the light in the useful zone defined as the 0 to 60 degree area.
Given the foregoing, it will be appreciated that a luminaire optical system is needed which provides lower operating temperature and therefore increased life, high total output and efficiency, increased useful light and decreased glare.